It says to de-possess a character you have to press backspace. But from looking in the manual it only tells you what the possession does, not what the controls are.

I've searched online and there is no mention of it!

I tapped various buttons, and i couldn't find it. So frustrating!

EDIT: Figured it out. It's the delete key to jump out of a body, and right control button to fly into a character.

use the jump button (default left or right shift or control - can't remember exactly) repeatedly to flap your little wings, make sure you approach them from behind aiming for the head.